Internal combustion engines for vehicles are known, comprising a head having one or more cylinders, inside which the engine cycle is carried out, and which are put in communication with respective combustion chambers of the engine itself. Suitable seats are further made on said head intended to put the combustion chamber in communication with ducts adapted to introduce a mixture of unburnt fuel and air in said chamber (“intake ducts”), and to remove the flue gases (“exhaust ducts”) from said combustion chamber.
The flows from and towards each combustion chamber are controlled by appropriate valves acting on said seats. In particular, each valve essentially comprises a guide element fixed within a cavity of the engine head and a stem slidably movable in opposite directions within a through seat defined by the guide element and bearing a closing portion at one end to close the connection between the relative intake or exhaust duct and the corresponding combustion chamber.
The opposite end of the valve stem axially protrudes from the relative guide element and is adapted to receive driving forces from a relative control device, such as a camshaft.
The valve stem is axially loaded by a cylindrical helical spring in the closing direction of the connection between the relative intake or exhaust duct and the corresponding combustion chamber.
In particular, the spring is mounted coaxially around the valve and is axially interposed between a fixed surface formed on the engine head and a plate fixed to the valve stem in the proximity of or at the end of the stem itself cooperating with the control device.
Sealing gaskets are normally fitted on the valves of the type described above for the lubricant oil normally circulating in the engines. Such gaskets, in one of the most commonly known shapes, include a support or reinforcement member, having a substantially tubular shape and made in a single piece of metal material, and an annular seal element, made of elastomeric material and interposed between the support member and the valve.
In particular, the seal element typically comprises a first portion adapted to cooperate, through an inner radial surface thereof, with the outer radial surface of the portion of the guide element facing in use said control device, and a second portion adapted to cooperate directly with the valve stem.
The gaskets of the type described above are widely used on all internal combustion engines to control the amount of lubricating oil that flows from the distribution area to the combustion chambers. An excessive flow of lubricating oil, in addition to an obvious excessive consumption of the oil itself, causes a deterioration of the engine efficiency and a reduction in the performance of the vehicle catalyst. On the other hand, an insufficient flow causes an increase of wear and noise of the valves accompanied by the presence of local temperature peaks. These phenomena may lead to a premature failure of the valves consequent to the seizure of the stem of the valves themselves inside the guide element.
The known gaskets allow, through the first portion of the seal element acting on the guide element of the relative valve, the achievement of a static seal and, through the second portion of the seal element cooperating with the stem, the achievement of a dynamic seal.
In particular, the static seal must ensure a certain degree of radial compression on the guide element in order to prevent the leakage of lubricant oil towards the combustion chambers and at the same time keep the gasket itself in position, while the dynamic seal is designed to allow the minimum oil flow needed to lubricate the coupling between stem and guide element.
In order to reduce the sliding friction against the stem, a ring of a low friction coefficient material, such as PTFE, cooperates with the second portion of the seal element.
The support member includes: a main portion, substantially cylindrical; a first annular flange, extending radially inwards from an axial end of the main portion and partly embedded in an annular seat of the seal element; and a second annular flange extending radially outwards from one opposite axial end of the main portion.
The support member further allows keeping into operation the gasket in the desired position on the valve.
The need is felt in the field to have gaskets having the maximum flexibility as regards the shape of the support member and/or the relative position of the support member with respect to the seal element and/or the fulfillment of the static and dynamic seal functions of the support member and/or the seal element.
U.S. Pat. Nos. 4,773,363, 6,227,548 and US-A-2006/027977 describe a gasket according to the preamble of claim 1.